1. Field of the Invention
The present invention relates to an internal combustion engine control apparatus having a thermal air flow rate measuring apparatus, and relates to an internal combustion engine control apparatus having a thermal air flow rate measuring apparatus which detects the flow rate of air flowing through an intake passage on the basis of, for example, a signal from a heating resistor.
2. Background Art
Conventionally, in an internal combustion engine control apparatus for an automobile or the like, an air flow rate measuring apparatus is arranged at an intake pipe of the internal combustion engine in order to detect the intake air flow rate of the internal combustion engine, and the fuel injection amount is controlled by using the air flow rate measured by the air flow rate measuring apparatus. Also, in recent years, it has been an important problem to improve the exhaust performance of the internal combustion engine, and it has become common to convert outputs of various sensors into digital values, on the basis of which the fuel injection amount is controlled by means of a digital arithmetic unit.
In the internal combustion engine, the air column phenomenon referred to as pulsation is generated by the resonance of an air pressure vibration caused by vertical movement of a piston, and a natural frequency vibration of the intake pipe. When the opening of a throttle valve installed in the intake pipe is increased, the amplitude of pulsation is increased.
Usually, air flows into a cylinder from an air cleaner. However, there is a case where air flows from the intake valve of the internal combustion engine to the air cleaner, and this phenomenon is referred to as reverse flow. When the reverse flow is measured by an air flow rate measuring apparatus which is not provided with the function to detect the reverse flow, the flow rate is measured as the forward flow rate regardless of the flow direction, and hence an error is caused in the air flow rate.
In order to solve this problem, an air flow rate measuring apparatus having a reverse flow detecting function is also available. Generally, many of the air flow rate measuring apparatuses having the reverse flow detecting function are a thermal type, and have characteristics in which the output level on the forward flow side is high and in which the output level on the reverse flow side is low.
It is known that in the thermal air flow rate measuring apparatus, an error is caused, at the time of pulsation, between the average flow rate of air actually taken into the cylinder and the average value of the air flow rate calculated by the digital arithmetic unit, due to the influence of a response delay caused by the heat capacity of the thermal air flow rate measuring apparatus itself, and due to the influence of a non-linear correspondence relationship between the air flow rate and the output of the thermal air flow rate measuring apparatus.
Further, it is known that as the fluid behavior at the time when the air flowing through the intake pipe is made to reversely flow, a phase shift is caused between the flow near the pipe wall surface and the main flow. In many cases, the element section of the thermal air flow rate detecting apparatus capable of detecting the reverse flow has a planar shape, and hence generates an error because, at the element section, a similar fluid behavior is caused between the main flow and the flow near the wall surface.
As a method to reduce the error due to the influence of the non-linear correspondence relationship among the above described influences, there is proposed in JP Patent Publication (Kokai) No. 2002-295292A a technique in which the air flow rate region that includes the reverse flow region and that is equal to or lower than a minimum air flow rate q0 is corrected on the basis of an air flow rate conversion table for converting an output signal of the air flow rate measuring apparatus into an air flow rate.